28 PRACTICAL HORSESHOEING. 



and the space measured between the white zone within it 

 and its outer surface gives its exact thickness. This is a 

 fact not without interest to the farrier in the operation of 

 attaching the shoe by nails, as these have to be driven only 

 through this dense horn — which in good hoofs cannot be 

 said to much exceed half an inch in thickness — and in pro- 

 portion to its thinness is the necessity for carefulness and 

 address on his part, in order to guard against wounding or 

 bruising the sensitive textures. 



The sole is more or less concave from its junction with 

 the wall ; nevertheless, even on moderately firm ground, 

 a portion of its circumference, which is generally the thick- 

 ness of the wall, takes a share in relieving the latter of 

 pressure. This is also a fact to be borne in mind. In soft 

 ground, the whole of its lower surface is made to aid in 

 sustaining the weight and prevent the foot sinking. But 

 it must be noted that the pressure of the lower face of the 

 pedal bone on the upper surface of the sole can never be 

 very great, else the sensitive membrane between them 

 would be seriously injured. This injury is prevented by 

 the coronary, and, to a lesser extent, by the plantar cush- 

 ion, which largely retard the descent of the bone on the 

 floor of the horny box. 



The frog, on both hard and soft ground, is an essential 

 portion of the weight-bearing face. In the unshod, 

 healthy foot it always projects beyond the level of the 

 sole, and seldom below that of the wall at the heels ; in- 

 deed, it is found, in the majority of hoofs, either on a 

 " level with the circumference of this part, or beyond it, so 

 that its contact with the ground, is assured. Hence its 

 utility in obviating concussion, supporting the tendons, 

 and, on slippery ground, in preventing falls. In pulling 

 up a horse sharply in the gallop, or in descending a steep 

 hill, the frog, together with the angular recess formed by 

 the bar and wall at the heel of the hoof, are eminently 



